Stardew Valley should be great for a 10yo, especially if she liked Animal Crossing.

Despite what several people are saying, the Deck isn’t “intended” for anyone with a certain number of Steam games.

You don’t need to own a certain # of games, you just need to want to play them in a handheld form factor like the Switch. I bought it because I wanted to play PC games on something that felt like a Switch. Being able to mod games and do other things that require access to system files was important to me.